This is part 2 of the series. If you have not gone through part 1, please refer to below
Continuing to the previous discussion on the Motor specifications, requirements and testing, let us continue on the next set of important parameters for motor design / selection
- Maximum Torque Endurance - To evaluate and rank the strength for the components – motor shaft key, rotor fixture, shaft tightening part, and stator fixtures – which are affected by mechanical fatigue by repeating the intermittent maximum torque of the motor. The parts should not have any defects or deterioration more than acceptable limits after defined endurance cycles of maximum torque.
- Overspeed – As motor is directly coupled to wheel (with or without gearbox), in case of downhill or some other circumstances motor RPM can go more than motor maximum RPM specification. So every motor should be tested for the Overspeed condition based on the usage scenario.
- Generator Mode – When brake is applied and inverter drive is disconnected or when motor running RPM is more than driving RPM, motor acts as generator – called regeneration. Motor performance may not be same when it acts as Generator and should be verified to decide the battery and inverter loading in case of Re-Generation mode.
- Reverse Mode – Normally motors are tested in forward mode and the power, torque, efficiency characteristics are evaluated in forward mode. But many Inverters have reverse mode also. The motor performance may be different and shall be tested to determine what maximum reverse speed shall be allowed.
- Temperature Rise – Motor specifications give max power and torque, but beware that those values are in ideal condition. Motor performance and efficiency does change based on temperature. So test your motor at maximum environment temperature (many places ambient temperature is as high as 40degC). This will give you practical power, torque range of motor for allowable maximum temperature and will also tell you what cooling is required. Inverter shall also take care of dynamically changing thresholds based on motor temperature.
- Supply Voltage – Motor is tested at the nominal voltage of 48 / 60 / 72 / 96 / 300 / 600V etc. (nominal system voltage). And believe me that this is not at all sufficient to understand your power curves. Weird right? Battery voltage to motor is never same. E.g. for 48V, the voltage can vary from 40 to 58.8V, which is a very high +/-20% variation from nominal value, and so the performance of the motor. So you know now what to do.
- Vibration – Every motor has vibrations, harmonics, resonance. And most of the motor manufacturers do not give/have this data. You must know these values and your mountings and isolators must be designed to take care of this. There is definitely a limit to which the maximum vibration amplitude is allowed. If you have the gearbox, axle; this becomes more important and complicated. So test it if you cannot calculate.
- Motor Imbalance – Each motor needs balancing to be done as a part of production process. Imbalance always creates high vibrations at 1x RPM. So before fitment it must be tested for any imbalance, else sent back for balancing.
- Noise measurement – Any moving machine makes noise. So if you have noise limits specified for your vehicles, test the motor for all conditions no load, fully loaded, max RPM, reverse etc. for the noise generated. Sometimes frequency and amplitude of this noise also becomes important as it may be annoying for user in certain operating conditions. Also dont forget to load your motor in lateral/axial torques in case of braking, vibration, sudden acceleration, axle loading and many other conditions.
Oops, we still not talked about Environmental and ?Electrical considerations ! Let’s see them in next and last part.
And again – There are many such points to be considered for choosing or designing your Electric Vehicle motor, which most of the people do not consider (again I said Most of the people :-)).
Give your feedbacks and comments. See you back in third and last part of this topic.
Jaywant Mahajan ([email protected])
A mechanical engineer who believes electric mobility is the key to sustainability
3 年Thanks for sharing Jaywant ?? Good service you are doing
Consultant, Developer, Software Architect (> 25 years of IT experience) | Freelancer | Entrepreneur | Electronics Engineer
3 年Thanks for your post. My queries... How does one make sure the motor temperature is always kept under its optimum range and not overheating due to its continuous operation. What happens in case it exceeds its high-temperature rating and the motor is out of control or cooling fails, or from the safety point of view what precautionary measures are taken care of by the control system. Stopping it abruptly can't be a solution as it is a risk to the rider.
Powertrain Engineer- 1D System Simulation | Model Based Development | Programming | Vehicle Dynamics
3 年Insightful, Thanks for sharing
Embedded Enthusiasts
3 年Thanks for posting
Energy Storage and Solar Assisted Air Conditioning Solution Provider
3 年Another fantastic post Jaywant. All motors are not created equal. Few delve into the specific tolerances in your post. Of particular interest is the relationship between torque variations to the motor mounts to the foundation containing these varying forces. Please give us more!!!